In vehicle construction, for example in the aircraft industry, fastening elements are used e.g. for claddings which have to meet special requirements. In order to avoid machining steps during final assembly, panel-shaped elements are e.g. provided with preliminary bores and, prior to final assembly, are provided with clips or inserts, which comprise further screwing elements attached with a certain amount of play. These screwing elements or snap-on holders are then, during final assembly, engaged by connectors or fasteners to other cladding elements/structural bearing elements. The panel-shaped elements or components are, in this case, often lightweight wall elements or sandwich panels, which for weight reasons are formed of two outer layers (from plastic or aluminium) in most cases, which are glued to a honeycomb-shaped stiffening arranged in between.
A clip 10 of this kind is shown in FIG. 1. This is basically shaped as a clamp with a first leg 11 and a second leg 12 with connecting web 13. To assemble it the clip is pushed onto a plate (18, only hinted at), so that a fastening element 20 comes to lie on a prepared opening in the plate (hidden in FIG. 1). This fastening element 20 (not visible in FIG. 1) essentially consists of a plate-shaped base with two nibs (projections 14, 15) and a nut part 21. The two projections 14, 15 are each held in a frame/by a bracket 16, 17 spanning the nibs, of the side cheeks 19, 22 of the upper leg 11 of the clip. The frames are designed in such a way that the fastening element 20 has lateral play, but cannot drop out of the clip.
The type of fastening which the fastening element 20 allows, may be realised in many variants, for example as a releasable or non-releasable locking connection with one or more locking stages. Furthermore the cylindrical section 21 may comprise a female thread for a screw. In this case a screw connection has the advantage that it is releasable and that the tightening torque can be controlled. The fastening element 20 can, depending on the profile used, be manufactured from metal or plastic.
If using a lightweight construction fastener, a fastener is passed (from below in FIG. 1), during its assembly, through a recess in the leg 12, a covered opening in the plate 18 and a further opening in the upper leg 11 and connected there to the fastening element 20. The plate 18 is thus fastened to another element. This type of clip fastener is available in many variants with legs of different lengths, in different shapes and for different plate thicknesses.
U.S. Pat. No. 4,219,064 shows the basic principle of such a fastener from metal, the more recent U.S. Pat. No. 6,474,917 shows an embodiment with a plastic clip and a fastening element from metal. In U.S. Pat. No. 4,219,064 the fastener is produced from a plate-shaped metal sheet part which is bent and punched according to constructional requirements. In a second production step the fastening element is inserted manually or in an automated manner into the clip body as such. The more recent U.S. Pat. No. 6,474,917 follows the same lines as regards basic layout and final assembly of the clip, but uses a special plastic for the clip body.
U.S. Pat. No. 6,474,917 describes this plastic as both strong and flexible, which meets the requirement profile for this plastic in this area. However, the structural-mechanical requirements for the clip are not the same in all cases. In those areas where the fastening element is to be inserted during final assembly, a certain elasticity is required, as is the case in those areas, which are subject to bending stress when the clip is pushed onto the plate 18. Other areas, by contrast, shall be very firm in order to stand up to robust handling of the clip during assembly. Moreover the clip must be able during assembly to absorb the torque of the pushed-in fastener, which is transferred from the fastening element 20 to the frames/brackets 16, 17, which is why these frames/brackets have to be designed in an appropriate manner.
In U.S. Pat. No. 6,474,917, in order to improve flexibility in the area of the web 13, it is proposed to weaken the wall thickness of the material, which supports the function of the web as a joint. This means however that the firmness at this point is, of course, reduced to the same extent.